New in version 4.0.0

January 8th, 2014

Improved Getting Started Experience:

The new spring.io website provides a whole series of "Getting Started" guides to help you learn Spring. You can read more about the guides in the Chapter 1, Getting Started With Spring section in this document. The new website also provides a comprehensive overview of the many additional projects that are released under the Spring umbrella.

If you are a Maven user you may also be interested in the helpful bill of materials POM file that is now published with each Spring Framework release.

Removed Deprecated Packages and Methods:

All deprecated packages, and many deprecated classes and methods have been removed with version 4.0. If you are upgrading from a previous release of Spring, you should ensure that you have fixed any deprecated calls that you were making to outdated APIs.

Java 8 (as well as 6 and 7):

Spring Framework 4.0 provides support for several Java 8 features. You can make use of lambda expressions and method references with Spring’s callback interfaces. There is first class support for java.time (JSR-310) and several existing annotations have been retrofitted as @Repeatable. You can also use Java 8’s parameter name discovery as an alternative to compiling your code with debug information enabled.

Spring remains compatible with older versions of Java and the JDK: Concretely, Java SE 6 (specifically, a minimum level equivalent to JDK 6 update 10, as released in late 2008) and above are still fully supported. However, for newly started development projects based on Spring 4, we recommend the use of Java 7 or 8.

Note that the Java 8 bytecode level (-target 1.8, as required by -source 1.8) is only fully supported as of Spring Framework 4.0. In particular, Spring 3.2 based applications need to be compiled with a maximum of Java 7 as the target, even if they happen to be deployed onto a Java 8 runtime. Please upgrade to Spring 4 for Java 8 based applications.

Java EE 6 and 7:

Java EE version 6 or above is now considered the baseline for Spring Framework 4, with the JPA 2.0 and Servlet 3.0 specifications being of particular relevance. In order to remain compatible with Google App Engine and older application servers, it is possible to deploy a Spring application into a Servlet 2.5 environment; however, Servlet 3.0+ is recommended when at all possible.

Groovy Bean Definition DSL:

With Spring Framework 4.0 it is now possible to define external bean configuration using a Groovy DSL. This is similar in concept to using XML bean definitions, but allows for a more concise syntax. Using Groovy also allows you to easily embed bean definitions directly in your bootstrap code.

Core Container Improvements:

Spring now treats generic types as a form of qualifier when injecting Beans. For example, if you are using a Spring Data Repository you can now easily inject a specific implementation: @Autowired Repository customerRepository.

If you use Spring’s meta-annotation support, you can now develop custom annotations that expose specific attributes from the source annotation.

Beans can now be Ordered when they are autowired into lists and arrays. Both the @Ordered annotation and Ordered interface are supported.

The @Lazy annotation can now be used on injection points, as well as @Bean definitions.

The @Description annotation has been added for developers using Java-based configuration.

A generalized model for conditionally filtering beans has been added via the @Conditional annotation. This is similar to @Profile but allows for user-defined strategies to be developed.

CGLIB-based proxy classes no longer require a default constructor. Support is provided via the objenesis library which is repackaged inline and distributed as part of the Spring Framework. With this strategy, no constructor at all is being invoked for proxy instances anymore.

There is managed time zone support across the framework now, e.g. on LocaleContext.

General Web Improvements:

Deployment to Servlet 2.5 servers remains an option, but Spring Framework 4.0 is now focused primarily on Servlet 3.0+ environments. If you are using the Spring MVC Test Framework you will need to ensure that a Servlet 3.0 compatible JAR is in your test classpath.

In addition to the WebSocket support mentioned earlier, the following general improvements have been made to Spring’s Web modules:

You can use the new @RestController annotation with Spring MVC applications, removing the need to add @ResponseBody to each of your @RequestMapping methods.

The AsyncRestTemplate class has been added, allowing non-blocking asynchronous support when developing REST clients.

A new spring-websocket module provides comprehensive support for WebSocket-based, two-way communication between client and server in web applications. It is compatible with JSR-356, the Java WebSocket API, and in addition provides SockJS-based fallback options (i.e. WebSocket emulation) for use in browsers that don’t yet support the WebSocket protocol (e.g. IE < 10).

A new spring-messaging module adds support for STOMP as the WebSocket sub-protocol to use in applications along with an annotation programming model for routing and processing STOMP messages from WebSocket clients. As a result an @Controller can now contain both @RequestMapping and @MessageMapping methods for handling HTTP requests and messages from WebSocket-connected clients. The new spring-messaging module also contains key abstractions from the Spring Integration project such as Message, MessageChannel, MessageHandler and others to serve as a foundation for messaging applications.

Testing Improvements:

Almost all annotations in the spring-test module (e.g., @ContextConfiguration, @WebAppConfiguration, @ContextHierarchy, @ActiveProfiles, etc.) can now be used as meta-annotations to create custom composed annotations and reduce configuration duplication across tests.

Active bean definition profiles can now be resolved programmatically, simply by implementing a custom ActiveProfilesResolver and registering it via the resolver attribute of @ActiveProfiles.

A new SocketUtils utility class has been introduced in the spring-core module which enables you to scan for free TCP & UDP server ports on localhost. This functionality is not specific to testing but can prove very useful when writing integration tests that require the use of sockets, for example tests that start an in-memory SMTP server, FTP server, Servlet container, etc.

As of Spring 4.0, the set of mocks in the org.springframework.mock.web package is now compatible with Servlet 3.0. Furthermore, several of the Servlet API mocks (e.g., MockHttpServletRequest, MockServletContext, etc.) have been updated with minor enhancements and improved configurability.